House Speaker Nancy Pelosi's plan to bring a major climate and energy measure to the floor Friday has prompted a whirlwind of lobbying.

From President Obama to environmentalists and industry, everyone is weighing in on the 1,201-page bill ahead of what will be the chamber's first-ever vote on a cap-and-trade program for curbing greenhouse gas emissions.

Last night, 22 environmental groups sent a letter to every member of the House urging them to vote in favor of H.R. 2454, also known as the "American Clean Energy and Security Act of 2009."

"We believe this is one of the most important votes of our time," wrote the Sierra Club, Natural Resources Defense Council, National Wildlife Federation, League of Conservation Voters and other groups. "There are rare moments in American history when the urgency to act is clear, the stakes are high, the costs of inaction are untenable, and the need for courageous leadership is paramount. Now is one of those moments."

Also today, 20 U.S. companies and electric utilities published full-page ads in several Washington newspapers calling for the bill's passage.

Opponents are also readying themselves for the floor battle, with the Cooler Heads Coalition, an ad hoc group of scientific skeptics and legislative critics, planning a special meeting today to organize for the vote. "It's gonna be fun," Myron Ebell, director of energy and global warming policy at the Competitive Enterprise Institute, wrote in an e-mail announcing the meeting.

Prospects for the bill appear to be improving even though Pelosi and the legislation's lead sponsors still do not have agreement on some of the key details dealing with agriculture.

According to an E&E analysis of the House floor debate, Pelosi can count on about 170 reliable supporters in a push to achieve 218 votes. There are another 108 fence-sitters, including 81 Democrats and 27 Republicans.

House Majority Leader Steny Hoyer (D-Md.) told reporters today he spoke several times last night with Pelosi before deciding to pull the trigger on a floor debate this week on the climate bill.

Democrats still are negotiating on the bill, which Hoyer said could prompt him to push the floor debate back to early July. "We think we're close enough and I'm hopeful today we get these resolved," Hoyer said.

The top House Republican leader today also underscored the political stakes of the climate bill. Minority Leader John Boehner (Ohio) used his outside political arm, the Freedom Project, to rail against the legislation.

Boehner sent a letter to House GOP members calling the upcoming floor battle “one of the defining debates of the 2010 cycle.”

“The American people will remember this debate and will remember who stands up for them,” Boehner said.

The House Rules Committee meets Thursday afternoon to hear from lawmakers who want to offer amendments to the legislation during the floor debate. And Democratic sponsors of the legislation today released a six-page summary of the bill that describes changes made since approval last month in the Energy and Commerce Committee.

New items in the House bill include 1.05 percent of the allowances set aside annually for the Advanced Research Projects Agency-Energy, which would be used for research and development on innovative energy technologies. Also, the Energy Department would have authority under a new program to distribute allowances on a competitive basis to support renewable energy and energy efficiency programs administered by American Indian tribes.